WiFi keeps dropping out or so poor it’s causing calls to pixelate/sound to go

We’ve just switched to Virgin and the internet connection has been completely awful. We both WFH and have regularly had to use our mobile data to have enough connection to run a Teams call without it dropping out. The broadband test says connection is fine, we’ve checked all the plugs are in, makes no difference. How can I get help with this? Or is just better to cancel and go with another provider?